Wireless communication using well casing

ABSTRACT

A petroleum well having a borehole extending into a formation is provided. A piping structure is positioned within the borehole, and an induction choke is positioned around the piping structure downhole. A communication system is provided along the piping structure between a surface of the well and the induction choke. A downhole module is positioned on an exterior surface of the piping structure and is configured to measure characteristics of the formation. The formation characteristics, such as pressure and resistivity, are communicated to the surface of the well along the piping structure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the following U.S. ProvisionalApplications, all of which are hereby incorporated by reference:

COMMONLY OWNED AND PREVIOUSLY FILED U.S. PROVISIONAL PATENT APPLICATIONSSerial T&K # Number Title Filing Date TH 1599 60/177,999 Toroidal Chokeinductor for Jan. 24, 2000 Wireless Communication and Control TH 160060/178,000 Ferromagnetic Choke in Jan. 24, 2000 Wellhead TH 160260/178,001 Controllable Gas-Lift Well Jan. 24, 2000 and Valve TH 160360/177,883 Permanent, Downhole, Wire- Jan. 24, 2000 less, Two-WayTelemetry Backbone Using Redundant Repeater, Spread Spectrum Arrays TH1668 60/177,998 Petroleum Well Having Jan. 24, 2000 Downhole Sensors,Communication, and Power TH 1669 60/177,997 System and Method for FluidJan. 24, 2000 Flow Optimization TS 6185 60/181,322 A Method andApparatus for Feb. 9, 2000 the Optimal Predistortion of anElectromagnetic Signal in a Downhole Communications System TH 1599x60/186,376 Toroidal Choke Inductor for Mar. 2, 2000 WirelessCommunication and Control TH 1600x 60/186,380 Ferromagnetic Choke inMar. 2, 2000 Wellhead TH 1601 60/186,505 Reservoir Production ControlMar. 2, 2000 from Intelligent Well Data TH 1671 60/186,504 TracerInjection in a Mar. 2, 2000 Production Well TH 1672 60/186,379 OilwellCasing Electrical Mar. 2, 2000 Power Pick-Off Points TH 1673 60/186,394Controllable Production Well Mar. 2, 2000 Packer TH 1674 60/186,382 Useof Downhole High Pres- Mar. 2, 2000 sure Gas in a Gas Lift Well TH 167560/186,503 Wireless Smart Well Casing Mar. 2, 2000 TH 1677 60/186,527Method for Downhole Power Mar. 2, 2000 Management Using Energiza- tionfrom Distributed Batteries or Capacitors with Reconfig- urable DischargeTH 1679 60/186,393 Wireless Downhole Well In- Mar. 2, 2000 terval Inflowand Injection Control TH 1681 60/186,394 Focused Through-Casing Re- Mar.2, 2000 sistivity Measurement TH 1704 60/186,531 Downhole RotaryHydraulic Mar. 2, 2000 Pressure for Valve Actuation TH 1705 60/186,377Wireless Downhole Measure- Mar. 2, 2000 ment and Control For OptimizingGas Lift Well and Field Performance TH 1722 60/186,381 ControlledDownhole Mar. 2, 2000 Chemical Injection TH 1723 60/186,378 WirelessPower and Commun- Mar. 2, 2000 ications Cross-Bar Switch

The current application shares some specification and figures with thefollowing commonly owned and concurrently filed applications, all ofwhich are hereby incorporated by reference:

COMMONLY OWNED AND CONCURRENTLY FILED U.S PATENT APPLICATIONS SerialFiling T&K # Number Title Date TH 1601 10/220,254 Reservoir ProductionControl Aug. 29, 2002 from Intelligent Well Data TH 1671 10/220,251Tracer Injection in a Aug. 29, 2002 Production Well TH 1672 10/220,402Oil Well Casing Electrical Aug. 29, 2002 Power Pick-Off Points TH 167310/220,252 Controllable Production Well Aug. 29, 2002 Packer TH 167410/220,249 Use of Downhole High Pres- Aug. 29, 2002 sure Gas in aGas-Lift Well TH 1677 10/220,253 Method for Downhole Power Aug. 29, 2002Management Using Energiza- tion from Distributed Batteries or Capacitorswith Reconfi- gurable Discharge TH 1679 10/220,453 Wireless DownholeWell Aug. 29, 2002 Interval Inflow and Injection Control TH 170410/22,326 Downhole Rotary Hydraulic Aug. 29, 2002 Pressure for ValveActuation TH 1705 10/220,455 Wireless Downhole Measure- Aug. 29, 2002ment and Control For Opti- mizing Gas Lift Well and Field Performance TH1722 10/220,372 Controlled Downhole Aug. 30, 2002 Chemical Injection TH1723 10/220,652 Wireless Power and Com- Aug. 29, 2002 municationsCross-Bar Switch

The current application shares some specification and figures with thefollowing commonly owned and previously filed applications, all of whichare hereby incorporated by reference:

COMMONLY OWNED AND PREVIOUSLY FILED U.S. PATNENT APPLICATIONS SerialFiling T&K # Number Title Date TH 1599US 09/769,047 Choke Inductor forWire- Oct. 20, 2003 less Communication and Control TH 1600US 09/769,048Induction Choke for Power Jan. 24, 2001 Distribution in Piping StructureTH 1602US 09/768,705 Controllable Gas-Lift Jan. 24, 2001 Well and ValveTH 1603US 09/768,655 Permanent Downhole, Jan. 24, 2001 Wireless, Two-WayTele- metry Backbone Using Redundant Repeater TH 1668US 09/768,046Petroleum Well Having Jan. 24, 2001 Downhole Sensors, Communication, andPower TH 1669US 09/768,656 System and Method for Jan. 24, 2001 FluidFlow Optimization TS 6185 09/779,935 A Method and Apparatus Feb. 8, 2001for the Optimal Predis- tortion of an Electro Mag- netic Signal in aDownhole Communications SystemThe benefit of 35 U.S.C. §120 is claimed for all of the above referencedcommonly owned applications. The applications referenced in the tablesabove are referred to herein as the “Related Applications.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to petroleum wells, and inparticular to a petroleum well having a casing which is used as aconductive path to transmit wireless spread spectrum communicationsbetween surface equipment and a downhole module used to measure physicalcharacteristics of a petroleum formation or condition of wellstructures.

2. Description of Related Art

Several methods have been devised to place electronics, sensors, orcontrollable valves downhole along an oil production tubing string, butall such known devices typically use an internal or external cable alongthe tubing string to provide power and communications downhole. It is,of course, highly undesirable and in practice difficult to use a cablealong the tubing string either integral to the tubing string or spacedin the annulus between the tubing string and the casing. The use of acable presents difficulties for well operators while assembling andinserting the tubing string into a borehole. Additionally, the cable issubjected to corrosion and heavy wear due to movement of the tubingstring within the borehole. An example of a downhole communicationsystem using a cable is shown in PCT/EP97/01621.

U.S. Pat. No. 4,839,644 describes a method and system for wirelesstwo-way communications in a cased borehole having a tubing string.However, this system describes a communication scheme for couplingelectromagnetic energy in a TEM mode using the annulus between thecasing and the tubing. This inductive coupling requires a substantiallynonconductive fluid such as crude oil in the annulus between the casingand the tubing. Therefore, the invention described in U.S. Pat. No.4,839,644 has not been widely adopted as a practical scheme for downholetwo-way communication. Another system for downhole communication usingmud pulse telemetry is described in U.S. Pat. Nos. 4,648,471 and5,887,657.Although mud pulse telemetry can be successful at low datarates, it is of limited usefulness where high data rates are required orwhere it is undesirable to have complex, mud pulse telemetry equipmentdownhole. Other methods of communicating within a borehole are describedin U.S. Pat. Nos. 4,468,665; 4,578,675; 4,739,325; 5,130,706; 5,467,083;5,493,288; 5,576,703; 5,574,374; and 5,883,516. Similarly, severalpermanent downhole sensors and control systems have been described inU.S. Pat. Nos. 4,972,704; 5,001,675; 5,134,285; 5,278,758; 5,662,165;5,730,219; 5,934,371; and 5,941,307.

Due to the limited success of wireless communication within a borehole,the current use of downhole measurement and control equipment isminimal. A lack of downhole measurement and control restricts theability to maximize economic return by optimizing production of thewell.

It would, therefore, be a significant advance in the operation ofpetroleum wells if an alternate means for providing communicationswithin a well were provided. More specifically, it would be advantageousif downhole physical characteristics of the formation could be easilycommunicated to the surface of the well. This information could then beused to increase the aggregate recovery of formation reserves, and wouldthereby optimize production of the well.

All references cited herein are incorporated by reference to the maximumextent allowable by law. To the extent a reference may not be fullyincorporated herein, it is incorporated by reference for backgroundpurposes and indicative of the knowledge of one of ordinary skill in theart.

BRIEF SUMMARY OF THE INVENTION

The problems associated with communicating in the borehole of apetroleum well are solved by the present invention. The metal wellcasing is used as a power and communications path between the surfaceand downhole modules, with a formation ground used as the return path tocomplete the electrical circuit. Communications are implemented usingspread-spectrum transceivers at the wellhead and at the downholemodules. The communications enable transmission of measurements fromdownhole sensors to the surface and control of downhole devices.

A petroleum well according to the present invention includes a downholemodule and a communications system. The downhole module is positioned onan exterior surface of a piping structure, the piping structure beingpositioned within a borehole of the petroleum well that extends into aformation. The downhole module collects formation data from theformation and communicates the data by using the communication system.The signals transmitted by the communication system are passed along thepiping structure.

A method for assessing a formation according to the present invention isapplied to a petroleum well having a borehole that extends into theformation. The petroleum well also includes a piping structure that ispositioned within the borehole. The method includes the step of sensinga formation characteristic within the formation and then communicatinginformation about the formation characteristic along the pipingstructure of the well.

A downhole module according to the present invention is adapted forcoupling to a piping structure of a petroleum well. The module includesa sensor that is used to sense a physical characteristic of a formationsurrounding the piping structure. A downhole modem is used to transmitdata representing the physical characteristic along the piping structureof the well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a petroleum well having a downhole moduleattached to a casing, the downhole module being configured to measureformation characteristics according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used in the present application, a “piping structure” can be onesingle pipe, a tubing string, a well casing, a pumping rod, a series ofinterconnected pipes, rods, rails, trusses, lattices, supports, a branchor lateral extension of a well, a network of interconnected pipes, orother structures known to one of ordinary skill in the art. Thepreferred embodiment makes use of the invention in the context of an oilwell where the piping structure comprises tubular, metallic,electrically-conductive pipe or tubing strings, but the invention is notso limited. For the present invention, at least a portion of the pipingstructure needs to be electrically conductive, such electricallyconductive portion may be the entire piping structure (e.g., steelpipes, copper pipes) or a longitudinal extending electrically conductiveportion combined with a longitudinally extending non-conductive portion.In other words, an electrically conductive piping structure is one thatprovides an electrical conducting path from one location where a powersource is electrically connected to another location where a deviceand/or electrical return is electrically connected. The piping structurewill typically be conventional round metal tubing, but thecross-sectional geometry of the piping structure, or any portionthereof, can vary in shape (e.g., round, rectangular, square, oval) andsize (e.g., length, diameter, wall thickness) along any portion of thepiping structure.

A “valve” is any device that functions to regulate the flow of a fluid.Examples of valves include, but are not limited to, sub-surface safetyvalves used to control fluid flow in well tubulars, and bellows-typegas-lift valves and controllable gas-lift valves each of which may beused to regulate the flow of lift gas into a tubing string of a well.The internal workings of valves can vary greatly, and in the presentapplication, it is not intended to limit the valves described to anyparticular configuration, so long as the valve functions to regulateflow. Some of the various types of flow regulating mechanisms include,but are not limited to, ball valve configurations, needle valveconfigurations, gate valve configurations, and cage valveconfigurations. Valves can be mounted downhole in a well in manydifferent ways, some of which include tubing conveyed mountingconfigurations, side-pocket mandrel configurations, or permanentmounting configurations such as mounting the valve in an enlarged tubingpod.

The term “modem” is used generically herein to refer to anycommunications device for transmitting and/or receiving electricalcommunication signals via an electrical conductor (e.g., metal). Hence,the term is not limited to the acronym for a modulator (device thatconverts a voice or data signal into a form that can betransmitted)/demodulator (a device that recovers an original signalafter it has modulated a high frequency carrier). Also, the term “modem”as used herein is not limited to conventional computer modems thatconvert digital signals to analog signals and vice versa (e.g., to senddigital data signals over the analog Public Switched Telephone Network).For example, if a sensor outputs measurements in an analog format, thensuch measurements may only need to be modulated (e.g., spread spectrummodulation) and transmitted—hence no analog-to-digital conversion isneeded. As another example, a relay/slave modem or communication devicemay only need to identify, filter, amplify, and/or retransmit a signalreceived.

The term “processor” is used in the present application to denote anydevice that is capable of performing arithmetic and/or logic operations.The processor may optionally include a control unit, a memory unit, andan arithmetic and logic unit.

The term “sensor” as used in the present application refers to anydevice that detects, determines, monitors, records, or otherwise sensesthe absolute value of or a change in a physical quantity. Sensors asdescribed in the present application can be used to measure temperature,pressure (both absolute and differential), flow rate, seismic data,acoustic data, pH level, salinity levels, valve positions, or almost anyother physical data.

As used in the present application, “wireless” means the absence of aconventional, insulated wire conductor e.g. extending from a downholedevice to the surface. Using the tubing and/or casing as a conductor isconsidered “wireless.”

The term “electronics module” in the present application refers to acontrol device. Electronics modules can exist in many configurations andcan be mounted downhole in many different ways. In one mountingconfiguration, the electronics module is actually located within a valveand provides control for the operation of a motor within the valve.Electronics modules can also be mounted external to any particularvalve. Some electronics modules will be mounted within side pocketmandrels or enlarged tubing pockets, while others may be permanentlyattached to the tubing string. Electronics modules often areelectrically connected to sensors and assist in relaying sensorinformation to the surface of the well. It is conceivable that thesensors associated with a particular electronics module may even bepackaged within the electronics module. Finally, the electronics moduleis often closely associated with, and may actually contain, a modem forreceiving, sending, and relaying communications from and to the surfaceof the well. Signals that are received from the surface by theelectronics module are often used to effect changes within downholecontrollable devices, such as valves. Signals sent or relayed to thesurface by the electronics module generally contain information aboutdownhole physical conditions supplied by the sensors.

In accordance with conventional terminology of oilfield practice, thedescriptors “upper,” “lower,” “uphole,” and “downhole” as used hereinare relative and refer to distance along hole depth from the surface,which in deviated or horizontal wells may or may not accord withvertical elevation measured with respect to a survey datum.

The term “formation” as used in the present application refers to a bedor deposit composed throughout of substantially the same kinds of rock.A formation may or may not contain petroleum products.

Referring to FIG. 1 in the drawings, a petroleum well 10 having awireless smart well casing 12 is illustrated. Petroleum well 10 includesa borehole 14 extending into a formation from a surface 16 to aproduction zone 18 that is located downhole. The casing 12 is disposedin borehole 14 and includes a structure of the type conventionallyemployed in the oil and gas industry. The casing 12 is typicallyinstalled in sections and is secured in borehole 14 during wellcompletion with cement 34. A tubing string, or production tubing, 26 isgenerally conventional comprising a plurality of elongated tubular pipesections joined by threaded couplings at each end of the pipe sections.Oil or gas produced by petroleum well 10 is typically delivered tosurface 16 by tubing string 26.

A production platform 27 is located at surface 16 and includes a tubinghanger 28. Tubing hanger 28 supports tubing string 26 such that thetubing string 26 is concentrically positioned within casing 12. Asillustrated in FIG. 1 production platform 27 also includes a gas inputthrottle 30 to permit the input of compressed gas into an annular space31 between casing 12 and tubing string 26. Conversely, an output valve32 permits the expulsion of oil and gas bubbles from an interior oftubing string 26 during oil production. While FIG. 1 illustrates a gaslift well, the present invention is not so limited, and the gas inputthrottle valve 30 and its associated input tubing is therefore optional.

Well 10 includes a communication system 44 for providing power andtwo-way communication signals downhole in well 10. Casing 12 acts as anelectrical conductor for communication system 44. In accordance with thepresent invention, an induction choke 42 is positioned concentricallyaround casing 12 prior to securing the casing 12 within cement 34.Induction choke 42 serves as a series impedance to electric current flowalong the casing 12. The size and material of lower induction choke 42can be altered to vary the series impedance value; however, the lowerinduction choke 42 is made of a ferromagnetic material. Induction choke42 is mounted concentric and external to casing 12, and is typicallyhardened with epoxy to withstand rough handling.

A means is provided to electrically insulate casing 12 and tubing string26 from ground connection through surface ancillary tubing connected tovalves 30 and 32. Insulators 40 provide this function as shown in FIG.1, but alternative methods exist and will be clear to those of averageskill in the art, such as the use of an insulated tubing hanger (notshown) in combination with an electrical isolation tubing joint (notshown). In alternative, another induction choke (not shown) can beplaced about the casing above the electrical point of connection 49 ofthe surface power and communication equipment 44, or two such chokes maybe placed individually about the production fluids tubing and the liftgas supply pipe. As noted in the related applications, inductive chokessuch as 42 external to the casing act to impede current flow on bothcasing and tubing at the points where these pass through such inductivechokes.

By electrically isolating a section of casing 12, power andcommunications signals can be supplied downhole along the casing 12 andtubing 26. While it is not an ideal electrical insulator, the cement 20can be of low electrical conductivity and provides a degree ofelectrical isolation between casing 12 and the formation surrounding thewell. Induction choke 42 further impedes current flow along casing 12and tubing 26, thereby allowing the signals to be passed betweeninduction choke 42 and the surface of the well. It is important to notethat electrical contact between casing 12 and tubing string 26 does notshort circuit the signals travelling along casing 12. Since tubingstring 26 is also located within the annulus of induction choke 42, thechoke 42 has the same electrical impedance effect on tubing string 26 ason casing 12. More specifically, current travelling down tubing string26 is effectively blocked from travelling further downhole to apotential ground. Similar protection is provided at the top of tubingstring 26 by insulating tubing joints 40. In practice the majority ofthe current conveyed into the well by the embodiment illustrated in FIG.1 is carried on the casing, and the tubing contributes negligibly to theconveyance of power to depth in the well.

A computer and power source 44 including a power supply 46 and a spreadspectrum communications device (e.g. modem) 48 is disposed outside ofborehole 14 at surface 16. The computer and power source 44 iselectrically connected to casing 12 at a current supply point 49 forsupplying time varying current to the casing 12. Computer and powersource 44 is grounded to surface 16. In operation the use of casing 12as a conductor is lossy because of the imperfect electrical isolationprovided by the cement 20. However, the spread-spectrum communicationstechnique is tolerant of noise and low signal levels, and can operateeffectively even with losses as high as −100 db.

As shown in FIG. 1, downhole electronics module 50 is positionedproximate to an exterior surface of the casing 12 prior to completion ofthe well. Downhole module 50 includes a plurality of sensors 70, 72, 74,for assessing formation characteristics (i.e. physical characteristics)about the formation that surrounds the well. These sensors could includeresistivity sensors, pressure sensors, temperature sensors, flow ratesensors, corrosion sensors, or geophones. Each of these sensors can beused to obtain information about the characteristics of the formation.Additionally, hydrophones could be used to measure acoustic waves inwell fluids within casing 12.

It is not obvious that sensors 70–74 would be able to measure formationcharacteristics such as pressure or resistivity, since they are embeddedwithin cement 34 and not in direct connection with formation 18.However, while the permeability of cement 34 is low, it does not providean absolute hydraulic seal. Since the flow of formation fluids throughthe cement is prevented by the casing 12, the pressure of fluids in thepore spaces of the cement 34 equilibrates with the pressure in theformation. Rapid changes in formation pressure cannot be measured, butslow changes can be measured, and it is data from slow changes as thereservoir is depleted that are valuable as an indication of reservoircondition.

The same considerations apply to other physical characteristics of theformation 18, such as fluid composition, which would be reflected inresistivity changes. The interpretation of such resistivity data differsfrom that for a conventional resistivity log of a well as measured byopenhole logging tools. Open-hole resistivity logs reveal the spatialvariation of resistivity over the logged section of the formation,measured at essentially a single instant of time. The resistivity logacquired by the methods of the present invention is derived from alocationally static single sensor, but over an extended period of time.In both cases, changes in the resistivity are the features which revealthe condition of the formation: in the open-hole log, these are spatialchanges, in the present invention, the changes are a function of timerather than spatial variations.

Downhole module 50 is configured to be mechanically connected to thecasing 12 either above or below induction choke 42. Electricalconnections to the downhole module 50 are provided by jumpers. Power isreceived at the downhole module 50 by a jumper connected to casing 12above the induction choke 42. A ground return jumper is provided thatconnects downhole module 50 to casing 12 below induction choke 42.

Downhole module 50 also includes a spread spectrum transceiver (notshown) for communicating with modem 48 at the surface of the well 10.The transceiver enables sensor data representing the formationcharacteristics to be transmitted to the surface of the well 10 for usein optimizing production of the well 10. If multiple downhole modules 50are positioned on the casing 12, the transceiver in each downhole moduleis able to communicate with transceivers in the other downhole modules,thereby allowing transceivers to relay signals and providing redundancyin the event of a failure of one of the downhole modules 50.

After positioning induction choke 42 and downhole module 50 on casing12, the casing 12 is run into borehole 14. Cement 34 is injected intothe annulus between the borehole and casing 12 to secure the casingwithin the borehole 14. The cement 34 also further secures thepositioning of the induction choke 42 and the downhole module 50relative to casing 12

Even though many of the examples discussed herein are applications ofthe present invention in petroleum wells, the present invention also canbe applied to other types of wells, including but not limited to waterwells and natural gas wells.

One skilled in the art will see that the present invention can beapplied in many areas where there is a need to provide a communicationsystem within a borehole, well, or any other area that is difficult toaccess. Also, one skilled in the art will see that the present inventioncan be applied in many areas where there is an already existingconductive piping structure and a need to route power and communicationsto a location on the piping structure. A water sprinkler system ornetwork in a building for extinguishing fires is an example of a pipingstructure that may be already existing and may have a same or similarpath as that desired for routing power and communications. In such caseanother piping structure or another portion of the same piping structuremay be used as the electrical return. The steel structure of a buildingmay also be used as a piping structure and/or electrical return fortransmitting power and communications in accordance with the presentinvention. The steel rebar in a concrete dam or a street may be used asa piping structure and/or electrical return for transmitting power andcommunications in accordance with the present invention. Thetransmission lines and network of piping between wells or across largestretches of land may be used as a piping structure and/or electricalreturn for transmitting power and communications in accordance with thepresent invention. Surface refinery production pipe networks may be usedas a piping structure and/or electrical return for transmitting powerand communications in accordance with the present invention. Thus, thereare numerous applications of the present invention in many differentareas or fields of use.

It should be apparent from the foregoing that an invention havingsignificant advantages has been provided. While the invention is shownin only a few of its forms, it is not just limited but is susceptible tovarious changes and modifications without departing from the spiritthereof.

1. A petroleum well having a having a borehole extending into aformation and a piping structure including a casing positioned withinthe borehole, the petroleum well comprising: a downhole modulepositioned on the outside of the casing for collecting formationcharacteristic data of the formation; a communication system operablycoupled to the piping structure and module such that the formationcharacteristic data can be communicated along the piping structure as atime-varying signal; and an induction choke external to the casingeffective to impede current flow through the casing, wherein thedownhole module receives power by a connection to the casing above theinduction choke and a ground return below the induction choke.
 2. Thepetroleum well according to claim 1, wherein the downhole moduleincludes a pressure sensor.
 3. The petroleum well according to claim 1,wherein the downhole module includes a flow rate sensor.
 4. Thepetroleum well according to claim 1, wherein the downhole moduleincludes a temperature sensor.
 5. The petroleum well according to claim1, wherein the downhole module includes a sensor for determining aresistivity value for the formation.
 6. The petroleum well according toclaim 1, wherein the downhole module includes a geophone for measuringacoustic waves.
 7. The petroleum well according to claim 1, wherein theinduction choke is positioned concentrically around the pipingstructure; and wherein the formation characteristic data is communicatedalong the piping structure between a current supply point and theinduction choke.
 8. In a petroleum well having a borehole extending intoa formation and having a piping structure positioned within theborehole, a method for assessing the formation comprising the steps of:sensing a formation characteristic of the formation using sensorsexternal to the piping structure; communicating the formationcharacteristic along the piping structure as a time varying signalapplied to the piping structure; and providing a lower induction chokepositioned concentrically around the piping structure; whereincommunicating the formation characteristic along the piping structure isdone between a current supply point and the lower induction choke. 9.The method according to claim 8, wherein the sensed formationcharacteristic is a formation fluid pressure.
 10. The method accordingto claim 8, wherein the sensed formation characteristic is a formationresistivity.
 11. The method according to claim 8, wherein the sensedformation characteristic is a formation fluid flow.
 12. The methodaccording to claim 8, wherein the sensed formation characteristic is aformation temperature.
 13. A method of constructing a petroleum wellhaving piping structure including casing, comprising the steps of:placing the casing within the borehole of the well; embedding one ormore sensors in the borehole external to the casing; positioning aninduction choke external to the casing effective to impede current flow;and providing a source of time-varying signals adapted for coupling tothe piping structure of the well.
 14. The method of constructing thewell of claim 13, including cementing the casing in the borehole for atleast a portion of thereof and embedding at least one of said sensors inthe cement.
 15. The method of constructing the well of claim 13,including operating the well comprising the substeps of: sensing aformation characteristic using one or more of said embedded sensors;communicating said sensed characteristic to a controller; changing anoperating parameter of the well based on said formation characteristic.16. The method of constructing the well of claim 13, including operatingthe well comprising the substeps of: sensing a formation characteristicusing one or more of said embedded sensors; communicating said sensedcharacteristic to a surface computer as a time-varying signal along thepiping structure.